1. Field of the Invention
The present invention relates generally to a digital camera, and more particularly, to a system in or usable with the digital camera for assisting the capture of text images. The system may be applied to handheld cameras and to mounted cameras.
2. Description of Related Art
It is well known to use scanners, such as flatbed scanners, to capture and convert bitmap images of documents to text or structured documents. An entire image can either be captured at maximum resolution, or a low-resolution pre-scan can be performed for selection of text regions, followed by a high resolution re-scan of the specified regions. In such a case, the document will always have a fixed optical relation to the scanner, and the resolution of the scanner is such that most documents can be captured with adequate resolution for optical-character-recognition (OCR) processing to convert the image to text.
However, a problem can occur for users of mounted or handheld digital cameras when capturing images of text documents. This is a relatively new area of use of digital cameras, of which not many users have experience. The problem is that the resolution of such cameras tends to be substantially less than that of flatbed scanners, and care is required to ensure that the captured image has sufficient resolution for OCR. There is a significant difference between the minimum resolution (visual resolution) at which a user can read the text in an image of a document, and the minimum resolution (OCR resolution) at which OCR will perform satisfactorily. The minimum OCR resolution is much greater than the minimum visual resolution.
For a camera, the size (or resolution) of the text characters in the image is directly dependent on the distance between the camera and the document being captured. Although experienced users may be able to judge this themselves, this tends to be a severe problem for novice users of the camera. For example, a novice user may be tempted to position the camera at a height at which he can just read the text in the field of view indicator. This would be too small for good OCR results, but the user would not find this out until he came to process the captured images. The image capture will be useless if the captured images cannot be processed for OCR. Moreover, once a user has encountered such a critical problem using a digital camera for the first time (instead of a traditional scanner), it is likely that he will never attempt to use the same system again.
Additionally, even when experienced users of digital cameras are confronted with a document with an extreme font size, they will often waste a lot of time repeatedly repositioning the camera until they achieve satisfactory results.
U.S. Pat. No. 6,473,523, filed May 4, 1999, entitled “Portable Text Capturing Method And Device Therefor”, which is incorporated herein by reference, discloses a system in which a handheld camera can provide feedback to the user about the suitability of an image for OCR. However, the suggested feedback is based on limited factors, which might not be directly representative if the text size in all cases. One of the problems is that the user generally requires an indication rapidly (in real time image capture), and so any processing must be performed very quickly. The described technique is to detect the spacing between lines of text. This can be processed relatively quickly, but as mentioned above, might not give an accurate determination of the text size in all cases. Moreover, the described feedback does not provide any guide as to better or corrective action the user should take to improve the image quality.